Quote from mathematician-poet
Solution 1:
Also, a similar quote is attributed to Paul Dirac (criticising Oppenheimer's interest in poetry):
"The aim of science is to make difficult things understandable in a simpler way; the aim of poetry is to state simple things in an incomprehensible way. The two are incompatible."
Solution 2:
You are probably thinking of J. Robert Oppenheimer quoting Paul Dirac in the first paragraph of an article entitled "The Age of Science 1900-1950", published in the September 1950 issue:
One evening more than 20 years ago Dirac, who was in Göttingen working on his quantum theory of radiation, took me to task with characteristic gentleness. "I understand," he said, "that you are writing poetry as well as working at physics. I do not see how you can do both. In science one tries to say some thing that no one knew before in a way that everyone can understand. Whereas in poetry ..."
The 10 reports here, to which these words may serve as introduction, do indeed attest that science says things that no one knew before in a way we can all understand.
Oppenheimer had published poems in the Harvard student literary magazine Hound & Horn, including one from 1928 called "Crossing" inspired by his time in the desert of New Mexico.